Not Much of an Engineer

by Stanley Hooker

  Lovesey set to work and eventually solved the problem with a redesign of the SU carburettor to what was known as the Diaphragm Carburettor. But this took some time, and in the meantime we were visited at Derby by Miss Shilling, who was a famous lady engineer from the Royal Aircraft Establishment. She brought with her a small metal diaphragm with a hole in the middle, to be fitted into the float chamber. This stopped the fuel bouncing to the top, while the hole passed sufficient fuel to keep the engine running. It was a most simple idea, and remarkably effective. It will ever be known as ‘Miss Shilling’s orifice’.

  Let me now add that the Germans paid a large penalty for their fuel injection. When the fuel is fed before the supercharger, as on the Merlin, it evaporates and cools the air by 25°C. This cooling enhances the performance of the supercharger, and increases the power of the engine, with a corresponding increase in aircraft speed, particularly at high altitude.

  By the end of 1942, my own work on the Merlin, sadly for me, had to end. Rubbra and Lovesey, the mainstays of the development, carried on; my supercharger and performance team passed to Oscar Wilde, who picked up the load with great skill and determination.

  When I look back, those first four years on the Merlin were the most satisfying, and, I think, the most important of my life, not only because the work had immediate relevance to the RAF in the war, but because they were my first steps down the road of becoming an engineer.

  For me, the future was to lie with the Whittle jet engine, and the enormous developments in aviation that stemmed thereafter.

  Chapter 3

  Jets

  I first met Frank Whittle in January 1940. At that time he was located with a small team of engineers at an old disused foundry at Lutterworth, near Rugby. His firm was called Power Jets, and the work he was doing was Top Secret. I was taken to see his first jet engine by Hayne Constant who, at that time, was the Director of the Engine Research Department of the Royal Aircraft Establishment at Farnborough. Constant had specialized in both centrifugal and axial compressors, and had frequently visited Derby to discuss with me the development of the Merlin supercharger. There was snow on the ground when he took me from Derby to Lutterworth, and I saw for the first time the strange jet engine roaring on its test bed. Compared to the sophisticated design and manufacture of Rolls-Royce, it looked a very crude and outlandish piece of apparatus. Yet, standing near to it while it was running, I felt conscious that I was in the presence of great power. Whether it was useful power or not, I had no idea.

  I cannot claim that I was an immediate convert to the jet engine. That took some months, while I did my own analysis of the gas-turbine engine and, more importantly, came under the spell of Frank Whittle’s genius and super technical knowledge.

  Whittle joined the RAF in 1923 as a ‘boy entrant’ and within three years his great ability got him to the new RAF College at Cranwell from which he was commissioned as a Pilot Officer. Even in those early days he had come to realise that the monopoly of the cumbersome piston engine in aircraft might be ended, and that far greater powers than could possibly be produced by such engines would be an enormous advantage in aviation. A lighter and faster-running engine was essential, and so his thoughts turned to the internal-combustion gas turbine. Whilst still a cadet he wrote a thesis on this subject, but this was so far ahead of contemporary practice on both engines and airframes that it was regarded as boyish ‘science fiction’.

  However, the powers that be in the RAF were sufficiently impressed to send him to Cambridge to take a degree in Mechanical Engineering. It was while at Cambridge that he began seriously to design his first jet engine, which combined two very important steps forward. The first was the elimination of the reciprocating motion of the piston engine, which only produces power on one of its four strokes. The other three are utilised for sucking in the charge, compressing it, and exhausting the burnt gases. I once facetiously remarked that the four-stroke engine has one stroke for producing power and three for wearing the engine out! By contrast, the gas-turbine engine produces power continuously by the simple process of compressing air, burning the fuel in the combustion chambers and then exhausting through the turbine which supplies the power to drive the compressor. After this turbine, the gas still has considerable pressure and temperature left, and thus the simple gas-turbine acts rather like a boiler. A boiler produces hot steam under pressure, and the gas-turbine hot gas under pressure.

  The second feature, of which Whittle was indisputably the inventor, was to use this pressurized hot gas in the form of a simple jet, the thrust of which would propel an aircraft. Thus, in one stroke, he eliminated both the propeller and the heavy gearing required to drive it. In doing so he swept away the factor which imposed a barrier to further advance in aircraft speed. Unlike the piston/propeller system the jet engine appeared able to propel an aircraft at any speed, and in fact the faster the better.

  The great impact that these two steps were to have on aviation was not immediately obvious. Whittle knew, because he had an unrivalled grasp of the fundamentals of thermodynamics and aerodynamics, and he never did anything until he had given it the deepest and most logical consideration. As I came to understand his work, I realised that he had laid down the performance of jet engines with the precision of Newton, a feat whose magnitude he never appeared to appreciate. For the preceding 30 years the performance of piston engines in flight was only known to a very rough approximation based on inaccurate empirical formulae, yet Whittle predicted what a jet engine would do before he had ever made one. Today, 40 years later, his formulae are used unchanged. They are of such precision that it is more accurate to calculate the performance of jet engines, including the most modern fan engines, than it is to attempt to measure it either in flight or in the astronomically costly test plants which attempt to simulate flight conditions on the ground. And this is true from take-off to the speed of Concorde, and beyond. Indeed, the pen really is mightier than the spanner!

  Whittle led the world in his thinking, so naturally he was subjected to the full blast of criticism from the sceptics and the illinformed. Gas-turbines were not new, of course, and for years A. A. Griffith and Constant had been considering them at the RAE. But they aimed to retain the propeller and merely to replace the piston engine by the gas-turbine as the power generator. In addition, Griffith was obsessed by the potential higher efficiency of the axial-flow compressor, as opposed to the simple centrifugal compressor which Whittle proposed to use. Constant also favoured the axial, but he had a more open mind. Sadly, however, these two key men, as principal advisers to the Air Ministry on engine matters, were no help to Whittle, and prevented him from getting financial aid from the Government to develop his engine until the late 1930s, after his titanic struggle had at last got the project going.

  Previous gas-turbines, which had all been land-based powerplants, had failed or been ineffective because of lack of knowledge about axial compressors, and especially, combustion chambers. Metals capable of maintaining their strength at the high temperatures in the engine were also in their infancy, although nickel alloy steels were pointing the way forward.

  Whittle was well aware of the potential advantages of the axial compressor, but with his infallible clear insight he chose a centrifugal compressor for his engine, on the basis that there was years of experience with them as superchargers on piston engines. They were also robust and strong, and relatively easy to manufacture. But a compressor of the size and performance he required had never been designed, so he set about this task himself and made a first-class job of it. He had had no experience, nor was there any he could draw from, so he was forced back to his own deep scientific understanding. He aimed at about 4:1 compression ratio, and 80 per cent efficiency, and incorporated in his design new and important features at the entry to the compressor and the diffuser. When, some years later, I was destined to take over from him and continue his work, I was never able to improve his compressor — I made it worse on one occasion, but never better.


  His first jet engine was made for him for next to nothing by the British Thomson Houston Co, at Rugby. Without their generous help he would never have got started, and we all owe a great debt of gratitude to the Directors and Chief Engineer of that great company, who had such faith in this young Air Force officer and his futuristic ideas.

  When I first met him, his first engine was running, and a second was being prepared for flight in May 1941. He had meagre facilities, a very small staff, and the minimum of financial assistance from the Department of Scientific Research of the Government. They had, however, instructed George Carter, Chief Designer of the Gloster Aircraft Co, to design and make the E.28/39 aircraft, as a suitable vehicle for the first flight of this new propulsion unit.

  Whittle was up to his ears with trouble with the combustion chambers, and with the reliability of the turbine blades. Both of these matters were outside my field, so we fell to discussing centrifugal compressors, about which subject I mistakenly thought that I was one of the world’s experts. But I soon realised that I was talking with my master.

  There was no test plant in the country powerful enough to run his compressor independently, and I discovered that Whittle had never seen a real test result on a centrifugal compressor. Accordingly, I took to him the latest and best results from tests on the Merlin blower, which he received with great joy, and began to analyse in his masterly fashion. And so, through the spring and summer of 1940 I visited him at Lutterworth, and saw his engine improving in reliability and performance to the stage where quite long runs could be made at 800 lb thrust.

  The significance of thrust as opposed to horsepower was not immediately obvious. Thrust is a force, and it only becomes power when the engine is moving with the aircraft. We at Rolls-Royce were used to thinking in horsepower, and it must be admitted that 800 lb thrust does not sound very impressive compared with 1,000 hp.

  One day in August 1940 I asked Hs if he would come down to Lutterworth to see this new engine. I described it to him and he said, ‘What does it do?’ I replied, ‘It is giving 800 lb of thrust’. Hs was not impressed, and said, ‘That doesn’t sound very much. It would not pull the skin off a rice pudding, would it?’

  But I was ready for this, and had done the sum. I said, ‘Do you know how much thrust the Merlin gives in a Spitfire flying at 300 mph?’ Hs shook his head, ‘No, how much?’

  ‘With its present propeller, which is only about 70 per cent efficient, it gives approximately 840 lb’, I replied.

  Hs leaned back in his chair, and reached back to the pushbutton on the wall behind him. His secretary came in.

  ‘I am going with Hooker to Lutterworth on Sunday’, he told her, and thus it was that he made that fateful trip, while the Battle of Britain was raging in the skies over southern England. This meeting was to transform the speed at which the jet engine was developed, and was destined ultimately to put Rolls-Royce into a commanding lead in the field of aviation gas turbines.

  Whittle personally conducted Hs around the plant at Lutterworth and explained to him his progress and ambitions. At the end of the tour Hs turned to him and said,

  ‘I don’t see many engines. What is holding you up?’

  Whittle explained the difficulties he had in getting certain components made, whereupon Hs said in his typical broadminded way, ‘Send us the drawings to Derby, and we will make them for you’. He said nothing about payment.

  And so it came to pass that the Derby Experimental Shop began making turbine blades, gearcases and other components for Whittle’s programme. In the following months Hs asked me and my colleague Lionel Haworth, from the Design Department at Derby, to keep in touch with the progress at Lutterworth.

  On 15 May 1941 Whittle’s W.1 engine flew in the Gloster E.28 aircraft, and the flight trials were a roaring success, as well as a source of amazement to those privileged to see them. The strange whistling roar of the engine, and the absence of the propeller or any other obvious means of propulsion, caused a great deal of speculation amongst the uninitiated onlookers. Was the aircraft pushed by the jet or sucked along by the intake? was the question on the lips of the uninitiated. Many thought it was was sucked along ‘like a bloody great vacuum cleaner’ as one RAF man was heard to say.

  When I began to lecture on the new jet engines after the war, this question continually arose. To demonstrate, I used to take with me a blown up balloon, and, at the appropriate time, used to release it when it would be blown into the audience by the escaping air jet.

  On one occasion I forgot to blow it up, and at the last moment nipped down to the men’s room to do so. I went into one of the cubicles, and was blowing it up when it burst with a loud bang. An amazed voice from a nearby cubicle called out ‘Are you all right in there?’ The mind boggled.

  Meanwhile, Whittle had been busy designing and making his W.2 engine which, with 1,600 lb of thrust, was to be twice as powerful, and was to be fitted to the first operational jet fighter built by Gloster Aircraft as the F.9/40, afterwards named the Meteor. He ran into new and unexpected troubles with the W.2, in that the compressor surged before the full power was developed. He was unable to get more than about 1,000 lb thrust before the surging set in, and the throttle had to be closed.

  Surging is caused by a sudden breakdown in the pressure developed by the compressor, in which case the airflow ceases to pass into the combustion chamber, but reverses and flows backwards through the impeller. Once the pressure in the chamber has been lost in this way, the compressor reasserts itself and the flow reverses itself again back to normality, whereupon the cycle repeats itself.

  To see this happen on the engine was quite horrifying. As the throttle was opened the engine would accelerate quite normally until suddenly there would be an enormous bang, and flames would come from out of the intake. The engine and all the instruments would give a large jerk; then the bang would repeat itself while the temperature would rise rapidly, and the throttle would have to be closed to prevent the engine destroying itself.

  The phenomenon of surging was well known in compressors, but there was no known means of predicting the conditions of airflow and pressure under which it would occur. The surge line on the graphical plot of performance, to the left of which the compressor behaved in this unstable way, had to be determined by testing the compressor independently, as we had done on the Merlin supercharger rig. But there was no test rig in Britain with sufficient power to test Whittle’s compressor, and so he was working totally in the dark.

  With Oscar Wilde, I proposed to him that we would build a test rig at Derby consisting of a 2,000 hp Rolls-Royce Vulture piston engine, driving through a 6:1 step-up gear, thus increasing the speed from 3,000 on the Vulture to the 18,000 rpm required by the W.2 compressor. This step-up gear was simply made by putting two Merlin propeller reduction gears in series and driving them backwards. Since each gear had a ratio of 0.42:1, when used in reverse it stepped the revolutions up by the inverse, that is by almost 2.5:1. Thus, two such gears gave more than 6:1 increase in rpm. In this way, we were able to measure the full performance of Whittle’s compressor, and I remember noting with envy and admiration that it had an efficiency of 79 per cent, within 1 per cent of Whittle’s theoretical figure.

  This rig made its contribution to the problem of surging on the W.2, which Whittle was gradually solving by cut and try methods. Its real value came in 1943 when Rolls-Royce had taken over the development of the jet engine at Barnoldswick in Yorkshire, and we were busy uprating it to 2,000 lb thrust in the Derwent I engine. But that story comes later.

  The W.2 was designed for the Gloster F.9/40 Meteor fighter, which was ordered by the Air Ministry in September 1940. Coincidentally, therefore, arrangements had to be made for the series production of the engine, for which Whittle’s facilities were totally inadequate. The Ministry of Aircraft Production got the Rover Car Co to undertake this task, with Whittle retaining design and technical control of the engine. The only changes that Rover were authorised to make were to be
minor ones in order to ease any production problems. Whittle never liked the details of this arrangement, nor did he think (unfairly in my opinion) that the Rover engineering team was good enough to produce his new baby.

  The main Rover facilities were fully stretched in producing and repairing Bristol aircooled piston aero engines, and so they had to find and equip another site for the jet work. They chose Bankfield Shed, a disused cotton mill at Barnoldswick on the borders of Yorkshire and Lancashire, midway between Clitheroe and Skipton. They turned this into a jet factory under their Production Engineer, Olaf Poppe, and housed their jet engineering team under their Chief Engineer, Maurice Wilkes, at Waterloo Mill in Clitheroe. As would be expected from their terms of reference, the facilities at Waterloo Mill were very meagre, and those at Barnoldswick were laid out to produce about 20 engines per month. Clearly the authorities were still uncertain about the importance of Whittle’s engine!

  Through their close connections on motor cars, Rover had sought the help of Joseph Lucas Ltd to produce the sheet-metal combustion chambers and jetpipes. Lucas laid down their facilities at nearby Burnley, under the management of John Morley.

  Because of the problems Whittle was having with the W.2, Rover waited long months for the definitive drawings to arrive in order that full production might begin. As time wore on, they decided to ignore their terms of reference, and began taking a hand in the development of the engine themselves at Waterloo Mill. This further strained the relations with Frank Whittle. Perhaps this was understandable, as he saw the control of his brainchild slipping from his grasp.

  I have often heard it said — indeed, it was the current view in many influential circles — that Frank Whittle was an awkward and difficult man to deal with. This I absolutely deny. In the more than 40 years that I have known him, we have never had a disagreement. Although Rolls-Royce were destined to take his engine away from him, I, personally, have never had anything but encouragement and generous help from him.